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SubjectRe: [PATCH v6 02/14] KVM: Cache as_id in kvm_memory_slot
On Mon, Mar 09, 2020 at 05:44:12PM -0400, Peter Xu wrote:
> Cache the address space ID just like the slot ID. It will be used in
> order to fill in the dirty ring entries.
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> include/linux/kvm_host.h | 1 +
> virt/kvm/kvm_main.c | 2 ++
> 2 files changed, 3 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index bcb9b2ac0791..afa0e9034881 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -346,6 +346,7 @@ struct kvm_memory_slot {
> unsigned long userspace_addr;
> u32 flags;
> short id;
> + u8 as_id;

My vote is to store this as a u16 and remove the BUILD_BUG_ON. Using a u8
doesn't save any memory since the compiler will pad out the struct.

> };
>
> static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memslot)
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 70f03ce0e5c1..e6484dabfc59 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1036,6 +1036,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>
> new = old = *slot;
>
> + BUILD_BUG_ON(U8_MAX < KVM_ADDRESS_SPACE_NUM);
> + new.as_id = as_id;
> new.id = id;
> new.base_gfn = base_gfn;
> new.npages = npages;
> --
> 2.24.1
>

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